Previous studies from this laboratory have demonstrated that dietary consumption of omega-3 fatty acids (FAs) can modulate arteiorlar resistance in normal rats and rats with renal ablation. Preliminary data is presented suggesting that omega-3 FAs modulate arteriolar tone by limiting the synthesis of TXA2, by altering the hydrolysis of phosphatidylinositol, or by modulating the expression of PKC-alpha. This proposal will elucidate the cellular basis of altered arteriolar tone by utilizing cultured glomerular muscle cells to study excitation-contraction coupling. As a basis for these studies, they have recently demonstrated decreased Angiotensin II (Ang II)-stimulated phosphorylation of the 20 kDa light chain (LC20) of myosin in mesangial cells enriched with eicospentaenoic acid (EPA). These findings were coupled with a parallel decrease in cell TXA2 synthesis. In aim #1, they will define the role of TXA2 in promoting Ang II-stimulated LC20 phosphorylation by using single test agents to selecting inhibit or excite TXA2 mediated LC20 phosphorylation. Since PKC-alpha may also be involved in Ang II stimulated LC20 phosphorylation and EPA appears to modulate its expression in vivo, they will also define the role of PCK-alpha in mediating Ang-II stimulated LC20 phosphorylation in aim #2. To elucidate PKC-alpha mediated responses from other events involved in excitation-contraction coupling, they have developed a mutant, catalytically inactive PKC-alpha (dominant-negative activity) and have successfully expressed the mutant enzyme in COS-7 and mesangial cells. Significant inhibition of PKC-alpha wild-type activity was attained. Two dimensional peptide mapping will complement these studies to explore site-specific alterations in phosphorylation, e.g., serine -1, 2 versus serine -19. Parallel experiments in kinase dead cells enriched with EPA will be performed to differentiate PKC-alpha independent versus dependent effects of EPA on excitation-contraction coupling. These studies will provide novel insights into the mechanisms which regulate excitation-contraction coupling in muscle cells and may provide a clue to the pathogenesis of altered arteriolar tone in hypertension, atherosclerosis and progressive renal disease.